Technical Field
The subject invention relates to monoclonal antibodies that may be used in the treatment and diagnosis of Alzheimer's Disease. In particular, the present invention relates to monoclonal antibodies referred to as 10F4 and 3C5 and to other monoclonal antibodies (e.g., murine, human or humanized) having similar properties thereto.
Background Information
In 1907, the physician Alois Alzheimer first described the neuropathological features of a form of dementia subsequently named in his honor as Alzheimer's disease (AD). In particular, AD is the most frequent cause for dementia among the aged, with an incidence of about 10% of the population in those above 65 years of age. With increasing age, the probability of disease also rises. Globally, there are about 15 million people affected with the disease and further increases in life expectancy are expected to increase the number of people affected with the disease to about three-fold over the next decades.
From a molecular point of view, Alzheimer's disease (AD) is characterized by a deposit of abnormally aggregated proteins. In the case of extra-cellular amyloid plaques, these deposits consist mostly of amyloid-β-peptide filaments, and in the case of the intracellular neurofibrillary tangles (NFTs), mostly of the tau protein. The amyloid β (Aβ) peptide arises from the β-amyloid precursor protein by proteolytic cleavage. This cleavage is effected by the cooperative activity of several proteases named α-, β- and γ-secretase. Cleavage leads to a number of specific fragments of differing length. The amyloid plaques consist mostly of peptides with a length of 40 or 42 amino acids (Aβ40, Aβ42). The dominant cleavage product is Aβ40; however, Aβ42 has a much stronger toxic effect. Cerebral amyloid deposits and cognitive impairments very similar to those observed in Alzheimer's disease are also hallmarks of Down's syndrome (trisomy 21), which occurs at a frequency of about 1 in 800 births.
The amyloid cascade hypothesis of Hardy and Higgins postulated that increased production of Aβ(1-42) would lead to the formation of protofibrils and fibrils (i.e., the principal components of Aβ plaques), these fibrils being responsible for the symptoms of Alzheimer's disease. Despite the poor correlation between severity of dementia and Aβ plaque burden deposited, this hypothesis was favored until recently. The discovery of soluble Aβ forms in AD brains, which correlates better with AD symptoms than plaque load does, has led to a revised amyloid-cascade-hypothesis.
Active immunization with Aβ peptides leads to a reduction in the formation as well as to partial dissolution of existing plaques. At the same time, it leads to alleviation of cognitive defects in APP transgenic mouse models. For passive immunization with antibodies directed to Aβ peptides, a reduction of an Aβ plaque burden was also found.
The results of a phase IIa trial (ELAN Corporation Plc, South San Francisco, Calif., USA and Dublin, UK) of active immunization with AN-1792 (Aβ(1-42) peptide in fibrillary condition of aggregation) suggest that immunotherapy directed to Aβ peptide was successful. In a subgroup of 30 patients, the progression of disease was significantly reduced in patients with positive anti-Aβ antibody titer, measured by MMSE and DAD index. However, this study was stopped because of serious side effects in the form of a meningoencephalitis (Bennett and Holtzman, 2005, Neurology, 64, 10-12). In particular, meningoencephalitis was characterized by neuroinflammation and infiltration of T-cells into the brain. Presumably, this was due to a T-cell immune response induced by injection of Aβ(1-42) as antigen. Such an immune response is not to be expected after passive immunization. To date, there are no clinical data with reference to this available. However, with reference to such a passive approach to immunization, concerns about the side effect profile were voiced because of preclinical studies in very old APP23 mice which received an antibody directed against an N-terminal epitope of Aβ(1-42) once a week over 5 months. In particular, these mice showed an increase in the number and severity of microhemorrhages compared to control animals treated with saline (Pfeifer et al., 2002, Science, 298, 1379). A comparable increase in microhaemorrhages was also described in very old (>24 months) Tg2576 and PDAPP mice (Racke et al., 2005, J Neurosci, 25, 629-636; Wilcock et al. 2004, J. Neuroinflammation, 1(1):24; De Mattos et al., 2004, Neurobiol. Aging 25(S2):577). In both mouse strains, antibody injection led to a significant increase in microhemorrhages. In contrast, an antibody directed against the central region of the Aβ(1-42) peptide did not induce microhemorrhages (de Mattos et al., supra). The lack of inducing microhemorrhages was associated with an antibody treatment which did not bind to aggregated Aβ peptide in the form of CAA (Racke et al., J Neurosci, 25, 629-636). Yet, the exact mechanism leading to microhemorrhages in mice transgenic for APP has not been understood. Presumably, cerebral amyloid angiopathy (CAA) induces or at least aggravates cerebral hemorrhages. CAA is present in nearly every Alzheimer's disease brain and about 20% of the cases are regarded as “severe CAA”. Passive immunization should therefore aim at avoiding microhemorrhages by selecting an antibody which recognizes the central or the carboxy terminal region of the Aβ peptide.
International Patent Application Publication No. WO2004/067561 describes stable Aβ(1-42) oligomers (Aβ(1-42) globulomers) and antibodies directed specifically against the globulomers. Digestion with unspecific proteases shows that the Aβ globulomer may be digested beginning with the hydrophilic N-terminus protruding from the globular core structure (Barghorn et al., 2005, J Neurochem, 95, 834-847). Such N-terminal truncated Aβ globulomers (Aβ(12-42) and Aβ(20-42) globulomers) represent the basic structural unit of this oligomeric Aβ and are a very potent antigen for active immunization of rabbits and mice leading to high antibody titers (WO2004/067561). The putative pathological role of N-terminally truncated Aβ forms in vivo has been suggested by several recent reports of their existence in AD brains (Sergeant et al., 2003, J Neurochem, 85, 1581-1591; Thal et al., 1999, J Neuropathol. Exp Neurol, 58, 210-216). During in vivo digestion, certain proteases found in brain, e.g. neprilysin (NEP 24.11) or insulin degrading enzyme (IDE), may be involved (Selkoe, 2001, Neuron, 32, 177-180).
In view of the above, there is a tremendous and immediate need for a treatment for Alzheimer's Disease which has few, if any, side effects (e.g., microhemmorhages). With such treatment, affected patients may be able to maintain a functional and active lifestyle for many years beyond that which is possible without such treatment. Thus, not only are there financial implications for such a treatment but “quality of life” implications as well, not only for the patients but also for their caregivers.
All patents and publications referred to herein are hereby incorporated in their entirety by reference.